1. Field of the Invention
The present invention relates to apparatuses and methods for defect replacement when an optical storage medium is read.
2. Descriptions of the Related Art
Most of optical storage media might have some defects in data area because of scratches, dusts, or fingerprints when exposing to a free environment. To recover the defects, the optical storage media provide an electronic structure to record defective addresses where defects are detected and spare area in which replacement data can be stored. For a conventional optical storage medium such as a compact disc, there are defect management areas (DMAs) to store replacements for the defects.
FIG. 1A shows a cross-sectional view of a one-layer compact disc. As FIG. 1A shows, the DMAs are implemented in an inner spare area (ISA) 101 and an outer spare Area (OSA) 103. The ISA 101 is allocated in an inner side of a valid data area 105, and the OSA 103 is allocated in an outer side of the valid data area 105. The valid data area 105 further comprises a user data area 109 for storing data. If there is any defect in the user data area 109, a corresponding replacement is stored in either the ISA 101 or the OSA 103. FIG. 1B shows a cross-sectional view of a two-layer compact disc. As FIG. 1B shows, each layer of the two-layer compact disc comprises the ISA 101, such as ISA 101A or 101B, and the OSA 103, such as 103A or 130B, for storing replacements.
One method of the prior art for defect replacement when a read operation is executed is shown in FIG. 2. Step 201 is executed to read a set of data from the user data area 109. In step 203, the optical access apparatus of the prior art determines if there is a defect in the set of data. If no, step 205 is executed to read another set of data. If yes, step 207 is executed to stop the reading. Step 209 is then executed to find a location of a corresponding replacement for the defect. After that, step 211 is executed to seek to the location to read the corresponding replacement. The defect is hence replaced by the corresponding replacement so the set of data has no defect now.
Another method of the prior art is shown in FIG. 3. When step 301 is executed, a set of data is read from the user data area 109 and stored to a first memory of the optical storage medium. In general, the first memory is a ring buffer. In step 303, the optical access apparatus of the prior art determines if there is a defect in the set of data. If no, step 305 is executed to read another set of data. If yes, step 307 is executed to record a current identification of the disc IDstart. Step 309 is then executed to read more sets of data continuously from the user data area 109 and store to the first memory until the first memory is full. Then step 311 is executed to record a current identification of the disc IDend. After that, step 313 is executed to seek addresses of all defects and corresponding replacements between IDstart and IDend. In step 315, the corresponding replacements are stored to a second memory of the optical access apparatus. Step 317 is then executed to copy the corresponding replacements stored in the second memory to the first memory. The defects are hence replaced by the replacements so the set of data has no defect now.
Though seek operations are common when data are reading from the optical storage media, the frequency of executing seek operations for the defect replacements is too high. Since the replacements are stored in the inner side or the outer side of the valid data area 105, such seek operations take a lot of time. Therefore, the speed of read decreases. Due to the above-mentioned drawback, a solution, especially for blu-ray discs, to efficiently execute defect replacement is needed in the industrial field.